Ink jet printers having one or more ink jet heads for projecting drops of ink onto paper or other printing medium to generate graphic images and text have become increasingly popular. To form color images, ink jet printers with multiple ink jet printing heads are used, with each head being supplied with ink of a different color. These colored inks are then applied, either alone or in combination, to the printing medium to make a finished color print. Typically, all of the colors needed to make the print are produced from combinations of cyan, magenta and yellow ink. In addition, black ink may be utilized for printing textual material or for producing true four-color prints.
In a common arrangement, the print medium is attached to a rotating drum and the ink jet heads are mounted on a traveling carriage that traverses the drum axially. As the heads scan paths over the printing medium, ink drops are projected from a minute external orifice in each head to the medium so as to form an image on the medium. A suitable control system synchronizes the generation of ink drops with the rotating drum.
In one basic type of ink jet head, ink drops are produced on demand. An exemplary drop-on-demand ink jet head is illustrated in U.S. Pat. No. 4,106,032 of Miura, et al. The Miura ink jet head has a two compartment ink chamber comprised of an inner horn compartment and an outer ink compartment separated by a horn compartment wall or first plate. These compartments communicate with one another through a first aperture or connecting channel which is provided through the horn compartment wall. Ink is delivered to the outer ink compartment of the ink jet head.
Whenever a drop of ink is needed, an electric pulse is applied to a piezoelectric crystal, causing the crystal to constrict. As a result, because the crystal is in intimate mechanical contact with ink in the horn compartment, a pressure wave is transmitted through the ink chamber. In response to this pressure wave, ink flows from the outer ink compartment and through an ink orifice passageway or second aperture. This orifice passageway passes through an ink chamber wall or second plate. Ink from the orifice passageway forms an ink drop at an internal ink drop-forming orifice outlet which is located at the outer surface of the ink chamber wall. An air chamber is provided adjacent to the ink compartment through which the ink drop from the orifice outlet travels. From the air chamber the ink drop passes through a main external orifice or third aperture which extends through an air chamber wall or third plate of the ink jet head. This latter orifice is coaxially aligned with both the first and second apertures and leads to the printing medium. Air under pressure is delivered to the air chamber and entrains the ink drop in a generally coaxial air stream as the ink drop travels through the air chamber. This air stream increases the speed of the drops toward, and the accuracy of applying the ink drops to, the print medium.
To reduce the length of the connecting channel and thereby enhance drop formation, the horn compartment wall is thinned in the region through which the connecting channel or first aperture passes. Typically, thinning is accomplished by removing material from the inner surface of the horn compartment wall. That is, material is removed from the surface which bounds the horn compartment to provide a dimple-like void or recess in this surface. As a result, the length of the first aperture or connecting channel is reduced. Similarly, the length of the second aperture or ink orifice passageway is reduced by removing material from the inner surface of the ink chamber wall. This forms another dimple-like recess in the portion of this wall through which the ink orifice passageway passes.
In one known manufacturing technique, the dimples are formed by chemically etching the horn compartment wall and the ink chamber plate. Thereafter, the connecting channel and ink drop-forming orifice passageways are punched or micro electrical discharge machined through the horn compartment plate and the ink chamber plate. The main external orifice of the ink jet head is then also formed through the air chamber plate in the same manner. These plates are thereafter attached to a body of the ink jet head. Attachment is performed under a microscope with a worker aligning the connecting channel, the ink orifice passageway and the external orifice as the ink jet head is assembled. This is an extremely labor intensive task. Also, it is very difficult to align the various apertures within required tight tolerances for operable ink jet heads. Therefore, the yield of satisfactory ink jet heads from this technique is in need of improvement.
In addition to etching, dimples have also been formed in ink jet head aperture plates by punching or stamping, such as disclosed in U.S. Pat. No. 4,282,533 of Brooks et al. However, this does not solve the problem of aligning apertures formed through the dimpled area of the various plates during assembly of the plates into an ink jet head. In addition, these approaches for forming recesses, as well as standard machining techniques, tend to produce tapered recesses. The thinnest portion of the plates are then at the relatively small pointed area or apex of the tapered recess. To provide apertures of the desired reduced length, the apertures must be formed at, or extremely close to, the pointed area of the recess. This further exacerbates the alignment problems. That is, the apertures not only must be properly aligned with one another, they also need to be aligned with the pointed area of the recesses.
As a further approach to manufacturing ink jet head aperture plates, a first sheet is provided with a first opening of a first dimension. A second much thinner sheet is brazed or otherwise fastened to the first sheet. A second opening, much smaller than the first opening, is drilled through the second sheet in substantial coaxial alignment with the first opening. In this method of manufacture, the first opening corresponds to the dimpled or thinned region of the overall aperture plate and the second opening corresponds to the aperture, as explained above. Again, the problem of aligning the various apertures as the ink jet head is assembled still exists in this approach. Furthermore, additional manufacturing steps are required to interconnect plural sheets to form each of the aperture plates.
Also, it has been proposed to form apertures through extremely thin plates rather than in dimpled or thinned regions of thicker plates. However, extremely thin aperture plates do not have sufficient rigidity for a number of applications. For example, difficulties are encountered when a single plate of this type is to be provided with plural apertures for use in an ink jet head array.
Ink jet heads of the non-air assisted type eliminate the air chamber plate and corresponding orifice. Because fewer orifices are required for this type of ink jet head, the difficulties of aligning multiple orifices are reduced somewhat. However, these difficulties are still present to some degree.
Therefore, a need exists for an improved method of manufacturing ink jet heads and ink jet head aperture plates, which is directed toward overcoming these and other disadvantages of prior art approaches.